The present invention relates to turbomachines and, more particularly, to improved means for locking rotor blades in rotor slots.
In the manufacture of bladed turbomachinery rotors, retention of the blades on a rotor, such as a turbine or fan rotor, has been commonly accomplished by insertion of metal strips within the rotor slot and subsequent bending of the ends of the metal strip such that the ends overlap the base of the blade and the radially extending faces of the rotor. These retainers have exhibited features which have proven to be undesirable. An example of one such undesirable feature is that loads tending to displace the rotor blade from its slot are absorbed by the bent ends of the metal strip. Since the metal strips have generally been designed to easily accommodate bending upon installation they are susceptible to bending in an opposite direction due to forces applied by the rotor blade.
Other undesirable features are associated with servicing of the rotor blade. Removal of the prior art devices during routine maintenance has proven troublesome since access, which in many instances cannot be conveniently provided, is required at both sides of the rotor disc. Furthermore, the prior art devices as described above are not suitable for re-use because of alterations in the physical and metallurgical properties associated with repeated bending of the ends of the retainers upon removal and re-installation of the blades. The attendant replacement of the retainers is costly, especially if a substantial number of blades must be removed for servicing.
Other prior art devices such as that shown in U.S. Pat. No. 3,832,092 have served generally to advance the state of the art in blade locking devices. However, such a device does not provide for load bearing members which fill available slot width to a maximum degree. Rather, since such members are rotated into the locking position, the cross-sectional area of such members are constrained by the height of the space between the rotor blade tang and bottom of the slot. Furthermore, these devices, while locking the blade generally within the rotor slot, do not provide means for preventing slight radial and angular movement of the blade within the slot. Such movement can result from machining the blade tang, rotor slot and locking device to within certain tolerances rather than to specific dimensions. Hence, when production parts are assembled into the slot environment, small radial and circumferential clearances occur between the parts which permit the aforementioned movement.